Line editors predate screen-based text editors and originated in an era when a computer operator typically interacted with a teleprinter (essentially a printer with a keyboard), with no video display, and no ability to move a cursor interactively within a document.
[1] Line editors are limited to typewriter keyboard text-oriented input and output methods.
In contrast, modern screen based editors allow the user to interactively and directly navigate, select, and modify portions of the document.
Line editors are still used non-interactively in shell scripts and when dealing with failing operating systems.
Update systems such as patch traditionally used diff data converted into a script of ed commands.